In general, there are two kinds of clinical thermometers. One utilizes the expansion and shrinkage effect of mercury and is named the mercurial clinical thermometer; its size is approximately as big as one half of a ballpoint pen. When taking the temperature it is usually put the patient's armpits. Another type of thermometer is the electronic type of clinical thermometer. The way of measurement is just the same as that of the mercurial type. The electronic clinical thermometer uses an electronic sensor to sense the temperature and displays it in digits. There are common disadvantages in the aforesaid two clinical thermometers. First, the patient must be asked to hole the thermometer in position so as to avoid its slipping from the measuring position. Secondly, these clinical thermometers cannot be used for long-time measurements, or for setting an alarm temperature.